Tick data is the data that displays all the changes of the price. For example, the price changed 36 times during 1 minute. If you use 1-min data then you will see only 4 prices of this bar: open, high, low and close.

If you use the tick data then in this particular case you will notice all 36 changes. The tick data gives you an opportunity to backtest the strategy as if you are trading on a real market.

This type of data is a must for all scalping strategies. It is also very useful for medium- and long-term strategies for getting the most qualitative results.